This invention relates to a resin encapsulated semiconductor device excellent in connection reliability between an electrode surface of an element and bonding wires particularly at high temperatures.
Recently as a packaging material for electronic parts mounting diodes, thyristors, transistors, IC, LSI, or VLSI, or these various semiconductor elements, there have been used plastic materials, particularly epoxy resins have been used mainly. Such resin packaged semiconductor devices occupy 80% or more of total semiconductor products.
Heretofore, the upper limit temperature of using these resin encapsulated semiconductor devices was about 125.degree. C. But with enlarged utility, there have been desired to use resin encapsulated semiconductor devices at higher temperatures. On the other hand, in order to increase a mounting density of parts, a packaging form is changed from a pin inserting type typified by dual inline plastic package (DILP), zigzag inline plastic package (ZIP), etc. to a surface mounting type typified by small outline package (SOP), flat plastic package (FPP), plastic leaded chip carrier (PLCC), etc. For mounting parts (soldering of parts), infrared rays and a vaper reflow method are employed. When the temperature of inside of package at the time of mounting is measured, it is about 100.degree. to 130.degree. C. at most in the case of the pin inserting type parts since a pointed end of lead inserted into a through-hole of a substrate is heated with solder.
In contrast, in the case of surface mounting type parts, since whole the package is heated with infrared rays and high temperature vapor, the inside of package is sometimes heated to such a high temperature as 215.degree. C. or more. In such a case, the heat time is as relatively short as several tens seconds. But such a high temperature is considerably severe to an epoxy resin used for packaging. For example, when subjected to such a heating treatment, various reliabilities are lowered compared with non-treated products. Various references, e.g. Proc. of the 27th Electronics Components Conference, pp 182-187 (1977), 22nd Annual Proceedings Reliability Physics, pp 37-47 (1984), IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol. CHMT-9, No. 4, pp 379-385 (1986), 25th Annual Proceedings Reliability Physics, pp 28-33 (1987), etc., report influences of halogens such as Br on gold-aluminum bonds, but there is disclosed no solution to improve gold-aluminum wire bond failure. From such a point of view, the development of resin encapsulated semiconductor devices good in heat resistance have been desired eagerly.